Rough Running GT-40

[Stickman]

I have a 98' Ski Nautique with GT-40 and approx 370 hours on it. It has run slightly "rough" since putting it in this Spring. It does not smell right when I'm skiing behind it as well - almost like it's running "rich". I have been doing the same decommissioning/ commissioning routine for the past 12 years and have never had this issue. I have added fresh gas and a can of Seafoam. I always use the marine Stabile in all of my gas. Spark Plugs are 3 years old with 30 hours on them. I have checked that all plug wires are connected. Plug wires are original. I hoping for some suggestions of things I can try since the closest dealer is far away. New plugs? new wires? Thanks for your input.

[vonzipper]

Check the pre pump volume, I had same issue last year, new pump and runs good as new, mine didn't show anything by checking fuel pressure, it only had a volume problem

[Stickman]

Check the pre pump volume, I had same issue last year, new pump and runs good as new, mine didn't show anything by checking fuel pressure, it only had a volume problem

Thanks vonzipper. The "roughness" is consistant from idle right up to 36 mph rpms. Did you experience the same with your fuel pump volume related issue? Thanks again.

[vonzipper]

I had the same rich running smell and poor performance, I removed my tank, checked the check valve, relays, and replaced my fuel filter, another thing is the short hose in the FCC, it's just 8mm hose with clamps, I had a vibrating needle on my fuel gauge when under load, at idle the needle was solid and at the right pressure

[charlesml3]

The "fresh gas" smell makes me think this is an ignition problem. First thing to do : Take the distributor cap off and look at the pads on the inside. I bet it's the original and they're all pitted out. Replace the cap and rotor if they look worn.

-Charles

[SilentSeven]

I recently was checking my new to me 97 and discovered some rust in the plug side ends of my ignition wires. Haven't replaced but they are on the list to do. Might be something to look at.

I concur that it sounds like ignition.

[nms1991]

what temperature is the engine running at? If it is not running any warmer than 145 F then i would suspect debris in the thermostat.

[Stickman]

Wow, I'm really hoping not to have to tear apart my gas tank. Although, I am tempted to siphon the tank dry in case there is excessive water.

The distributor cap, rotor, and wires are all original. I'll take a look a them and see if they show signs of wear/ corrosion. Otherwise, I hate to just start replacing parts that I'm not sure are bad.

Temperature has remained a steady 160 F.

Do you guys drain your FCC every year? I stripped the 1/8" NPT brass plug 2 year ago, so I have not been able to drain. Back when I did drain it every fall, always seemed like I just drained gas and no water. Does anyone know if that female 1/8" fitting the plug mates to just spins out, or is there more to it to remove?

Thanks for everyone's suggestions!

[charlesml3]

The distributor cap, rotor, and wires are all original. I'll take a look a them and see if they show signs of wear/ corrosion. Otherwise, I hate to just start replacing parts that I'm not sure are bad.

Oh come on, now. A cap and rotor for a GT-40 is $20 or so. Yours are 15 years old. Your hours are low but there's really no reason not to replace them at this point.

I know my boat behaved exactly the same way. 99 Air. Rough idle, skipping at speed, smell of raw gas at the exhaust. I took that opportunity to replace the cap, rotor, plug wires and plugs. All of that was less than $100 and it completely resolved the issue. I kept the old plug wires around for spares because they seemed fine.

-Charles

[Stickman]

Wow. I'm seeing $49 for the Cap/Rotor alone. Where are you buying your parts?

[SilentSeven]

...seems actually about right. Pony up or go cheap and try to R&R the cap yourself. Inspect for cracks, clean out any carbon traces and clean any corrosion off the contacts. Same for the rotor. Not as good as a new set but the budget way to see if you can make a difference.

[charlesml3]

> Wow. I'm seeing $49 for the Cap/Rotor alone. Where are you buying your parts?

Dude, you have several people here trying to help you sort this boat out, but every one of your responses is "I don't want to do that." It seems like you're much more interested in arguing with us than taking our advice to figure out what's wrong.

The PCM GT-40 that came in these boats in the late 90s or so would come with any one of about 4 different distributor caps and rotors. The set I bought for my 99 was right around $20. If yours is $49, who cares? That isn't even 1/2 a tank of gas.

If you want to get this boat going again, stop arguing and start troubleshooting. At 16 years old, it's time for a cap and rotor and that'll most likely resolve the issue.

-Charles

[vortech347]

Sounds like ignition. The cap and rotor are not really marine specific. So if you can find the Ford equivalent you could save a bit of money. The ignition wires may be specific as far as length on that motor but they won't be special for marine use either.

You could try a set from an 85 Broncho with 351 and see if they fit.

Also, the ignition coil could be going bad so that's another ignition item to check.

Even if it turns out that it's not ignition related all of the those items are not very expensive and it couldn't hurt to replace them. It's not like you are throwing big money parts at the boat.

[jhersey29]

At the lost days of skiing and added cost of a mechanic I would replace all the basics. They are all cheap and combine them to save freight. Cap, rotor, plug wires, plugs, coil, coil wire, fuel filter, and fuel relay. Heck maybe even low pressure fuel pump. These all have a history of common known failures. Save you old parts as spares. Not like your wasting money. Building a set of spare parts with the old ones never hurts.